fix: OPTIC-514: Dashboards page crashes when opened on project with n…

…o imported tasks (#5674)

### PR fulfills these requirements
- [X] Commit message(s) and PR title follows the format
`[fix|feat|ci|chore|doc]: TICKET-ID: Short description of change made`
ex. `fix: DEV-XXXX: Removed inconsistent code usage causing intermittent
errors`
- [ ] Tests for the changes have been added/updated (for bug
fixes/features)
- [ ] Docs have been added/updated (for bug fixes/features)
- [X] Best efforts were made to ensure docs/code are concise and
coherent (checked for spelling/grammatical errors, commented out code,
debug logs etc.)
- [X] Self-reviewed and ran all changes on a local instance (for bug
fixes/features)



#### Change has impacts in these area(s)
_(check all that apply)_
- [ ] Product design
- [ ] Backend (Database)
- [X] Backend (API)
- [ ] Frontend



### Describe the reason for change
When no tasks were imported for a project, the absence of the
completed_at annotation used in DataManager filters would cause errors
to be thrown. This properly annotates the None result to ensure there is
always a completed_at annotated field so that the filters do not break.

label_studio/data_manager/managers.py

@@ -6,6 +6,7 @@
 
 import ujson as json
 from core.feature_flags import flag_set
+from core.utils.db import fast_first
 from data_manager.prepare_params import ConjunctionEnum
 from django.conf import settings
 from django.contrib.postgres.aggregates import ArrayAgg
@@ -509,46 +510,61 @@ def __init__(self, expression, distinct=False, output_field=None, **extra):
         super().__init__(expression, distinct='DISTINCT ' if distinct else '', output_field=output_field, **extra)
 
 
-def annotate_completed_at(queryset):
-    if flag_set('fflag_feat_optic_161_project_settings_for_low_agreement_threshold_score_short', user='auto'):
-        return annotated_completed_at_considering_agreement_threshold(queryset)
-
+def newest_annotation_subquery() -> Subquery:
     from tasks.models import Annotation
 
-    newest = Annotation.objects.filter(task=OuterRef('pk')).order_by('-id')[:1]
-    return queryset.annotate(completed_at=Case(When(is_labeled=True, then=Subquery(newest.values('created_at')))))
+    newest_annotations = Annotation.objects.filter(task=OuterRef('pk')).order_by('-id')[:1]
+    return Subquery(newest_annotations.values('created_at'))
 
 
-def annotated_completed_at_considering_agreement_threshold(queryset):
-    from tasks.models import Annotation
+def base_annotate_completed_at(queryset: TaskQuerySet) -> TaskQuerySet:
+    return queryset.annotate(completed_at=Case(When(is_labeled=True, then=newest_annotation_subquery())))
+
 
+def annotate_completed_at(queryset: TaskQuerySet) -> TaskQuerySet:
     LseProject = load_func(settings.LSE_PROJECT)
     get_tasks_agreement_queryset = load_func(settings.GET_TASKS_AGREEMENT_QUERYSET)
 
-    if not queryset.exists():
-        # No tasks to annotate. Quit early
-        return queryset
+    is_lse_project = bool(LseProject)
+    has_custom_agreement_queryset = bool(get_tasks_agreement_queryset)
 
-    project_id = queryset[0].project_id
+    if (
+        is_lse_project
+        and has_custom_agreement_queryset
+        and flag_set('fflag_feat_optic_161_project_settings_for_low_agreement_threshold_score_short', user='auto')
+    ):
+        return annotated_completed_at_considering_agreement_threshold(queryset)
 
-    newest_annotation = Annotation.objects.filter(task=OuterRef('pk')).order_by('-id')[:1]
+    return base_annotate_completed_at(queryset)
 
-    if not LseProject:
-        # Not LSE so there will not be agreement_threshold-based task completeness
-        return queryset.annotate(
-            completed_at=Case(When(is_labeled=True, then=Subquery(newest_annotation.values('created_at'))))
+
+def annotated_completed_at_considering_agreement_threshold(queryset):
+    LseProject = load_func(settings.LSE_PROJECT)
+    get_tasks_agreement_queryset = load_func(settings.GET_TASKS_AGREEMENT_QUERYSET)
+
+    is_lse_project = bool(LseProject)
+    has_custom_agreement_queryset = bool(get_tasks_agreement_queryset)
+
+    project_exists = is_lse_project and hasattr(queryset, 'project') and queryset.project is not None
+
+    project_id = queryset.project.id if project_exists else None
+
+    if project_id is None or not is_lse_project or not has_custom_agreement_queryset:
+        return base_annotate_completed_at(queryset)
+
+    lse_project = fast_first(
+        LseProject.objects.filter(project_id=project_id).values(
+            'agreement_threshold', 'max_additional_annotators_assignable'
         )
+    )
 
-    lse_project = LseProject.objects.filter(project_id=project_id).first()
-    agreement_threshold = lse_project.agreement_threshold if lse_project else None
-    if not (get_tasks_agreement_queryset and agreement_threshold):
+    agreement_threshold = lse_project['agreement_threshold'] if lse_project else None
+    if not lse_project or not agreement_threshold:
         # This project doesn't use task_agreement so don't consider it when determining completed_at
-        return queryset.annotate(
-            completed_at=Case(When(is_labeled=True, then=Subquery(newest_annotation.values('created_at'))))
-        )
+        return base_annotate_completed_at(queryset)
 
     queryset = get_tasks_agreement_queryset(queryset)
-    max_additional_annotators_assignable = lse_project.max_additional_annotators_assignable
+    max_additional_annotators_assignable = lse_project['max_additional_annotators_assignable']
 
     completed_at_case = Case(
         When(
@@ -558,7 +574,7 @@ def annotated_completed_at_considering_agreement_threshold(queryset):
                 Q(_agreement__gte=agreement_threshold)
                 | Q(annotation_count__gte=(F('overlap') + max_additional_annotators_assignable))
             ),
-            then=Subquery(newest_annotation.values('created_at')),
+            then=newest_annotation_subquery(),
         ),
         default=Value(None),
         output_field=DateTimeField(),